1. Field of the Invention
The present invention relates to a method of correcting white balance in a video camera, and more particularly, to a method of correcting white balance in a video camera, in which it is judged whether data accumulated in each of unit cells of an input image signal is mixed color data when white balance correction is carried out for the input image signal, and the judged result is reflected in the correction process, thereby enabling more accurate white balance correction.
2. Discussion of Related Art
In general, a video camera is divided into color and monochrome types according as it recognizes colors or not, and classified into types for recording/storage (for home use and broadcasting use) and for monitoring according to its use. The video camera for recording/storage is called camcorder which usually includes camera, recording/playback part and monitor in a unit case. On the other hand, in the monitoring video camera system, its camera is separated from its recording/playback part and monitor. Accordingly, the video camera in the monitoring system generally means the camera other than the recording/playback part. In this specification, xe2x80x9cvideo cameraxe2x80x9d is used as a term which means the color video camera for recording/storage, that is, the camera of color camcorder, and color video camera for monitoring.
A video signal generated by the image capture device of the video camera passes through various signal processing steps, for example, automatic focus (AF) control or blooming prevention process, to be outputted to the monitor and VCR. These signal processing steps also include white balance correction. A method of correcting white balance is disclosed in, for example, U.S. Pat. No. 4,736,241 (Apr. 5, 1988) which proposed a hardware arrangement for detecting the variation in color temperature of illumination source of light from the color difference signal provided by the image capture device of the video camera and for processing red and blue signals according to the detected signal, thereby automatically controlling white balance.
The white balance correction in the video camera is called a function of automatically controlling the red gain and blue gain to allow the average of color difference signals rxe2x88x92y and bxe2x88x92y for the entire picture to be zero. Human eyes correctly perceive a white object to be white without regard to the variation in color temperature, for example, the variation from the blue light of autumn sky to the red light of the evening glow. However, the video camera using electric signals cannot provide the adaptability the human eyes have. Specifically, when the video camera takes a picture of a white object in the lightning of 3000[xc2x0K], and then takes a picture of the same object again in the lightning of 5000[xc2x0K] while the red gain and blue gain are controlled to allow the object pictured first to be seen white on the monitor, the object displayed on the monitor is seen blue not white. The white balance correction is used for solving this problem the video camera has.
A conventional method of processing the white balance correction in software includes the steps of, in the state that data corresponding to one picture captured is divided into a predetermined number of unit cells, accumulating color difference signals by unit cells, selecting an effective cell using blackbody radiation curve, and allowing the average of the color difference signals of the selected effective cell to be zero. However, the aforementioned conventional method of correcting the white balance in a video camera carries out white balance correction without judging whether the color of the effective cell is monochrome or mixed color, bringing about inaccurate processing result.
Accordingly, the present invention is directed to a method of correcting white balance in a video camera that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of correcting white balance in a video camera, in which, for each of unit cells a picture, it is judged whether its color is monochrome or mixed color on the basis of automatic focus data or the correlation between corresponding cell and its neighboring cells and the judged result is reflected in white balance correction, enabling more accurate white balance correction process.
To accomplish the object of the present invention, there is provided a method of correcting white balance in a video camera, which controls the red gain and blue gain of a captured image signal to allow the average of color difference signals of a picture, the method including the steps of (a) dividing the captured image of one picture into a predetermined number of unit cells, and accumulating the color difference signals by cells divided, (b) extracting an effective cell according as the accumulated data of each of the unit cells is data required for white balance correction or not, (c) judging whether data of the effective cell extracted in step (b) is monochrome data or mixed color data, (d) performing white balance correction without using the effective cell when the data of the effective cell is judged to be mixed color data in step (c), and (e) carrying out white balance correction using the effective cell when the data of the effective cell is judged to be monochrome data in step (c).
In the aforementioned method, the judgment whether data accumulated in each of the unit cells is data required for white balance correction or not is carried out according as the accumulated data exists in a predetermined region including blackbody radiation curve. The judgement whether data of the effective cell is monochrome data or mixed color data in step (c) is carried out according to the amount of AF data corresponding cell has or the correlation between corresponding cell and its neighboring cells.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.